The prior art aeration-type rotary dryer is known by U.S. Pat. No. 4,656,759. The dryer has inlet and outlet boxes, a rotary cylinder having opposite open end portions rotatably and air-tightly fitted in the inlet and outlet boxes, a means for rotating the cylinder, a feeder provided in the inlet box, an air duct having a uniform diameter and axially extending in the cylinder, a hot-air source supplying the axial duct with the hot air, a plurality of radial pipes branched from the duct, an exhaust and a discharge port each provided in the outlet box. The rotary cylinder is provided at its opposite ends with inlet and outlet partitions in the form of a hollow circular plate. The inlet partition is formed with a central opening through which pass the chute of the feeder and the air duct. The outlet partition is also formed with a central opening through which the used air and the treated materials are discharged to the outlet box.
The moist materials form a flow when fed into the cylinder. The flow would overflow to the inlet box if its depth is larger than the radial width or threshold height of the inlet partition. This means that the dryer is sometimes limited in capacity by the radial width of the inlet partition. The conventional aeration-type dryer requires the inlet partition thereof to have a relatively large central opening to receive the chute of the feeder and the air duct of a relatively large diameter, so that the inlet partition inevitably has a relatively small radial width or relatively low threshold. Therefore, it is limited to enlarge the radial width of the inlet partition in order to increase the feeding speed.
The materials, when treated, leave the cylinder to the outlet box through the central opening in the outlet partition threshold plate. The used air also exhausts from the same opening. The dryer can not have a larger capacity without increasing an amount of the exhaust air that is defined by an effective area of the opening in the outlet threshold. If the opening were diametrically enlarged to increase the amount of an exhaust air, the radial width or height of the threshold would become too low to keep the materials in the cylinder for a desired time, resulting in that the dryer would discharge the materials insufficiently treated. Besides, the dryer has another disadvantage that the outlet partition prevents lumps in the materials from discharging to the outlet box, because the radial width or threshold of the outlet partition is too high for the lumps to get over the outlet partition. The dryer has the radial pipes extending near to the surface or into the inside of the flow of materials to inject hot air to the materials from the outer ends of the pipes. However, it is not easy to always provide the radial pipes with outer ends thereof disposed at optimum positions to blow the hot air to the flow of materials. The reason for this is that the radial pipes are not angularly adjustable but fixed while the flow of materials has such a surface that is partially differently inclined in response to the physical properties of the materials as well as the rotational speed of the cylinder.
The present invention is intended to solve the problems as described above. It is therefore an object of the invention is to provide an aeration-type rotary dryer having a chargeable capacity increased by the use of an inlet partition with a small central opening.
It is another object of the invention to provide an aeration rotary dryer having an exhaust to be increased without enlarging a central opening in an outlet partition.
It is a further object of the invention to provide an aeration-type rotary dryer enabling to discharge lumps contained in materials without trouble.
It is still another object of the invention to provide an aeration-type rotary dryer having an air duct composed of successively connected tubular members of which the upstream is larger in diameter than the downstream, in order to adjust an amount of air injected from radial pipes branched from each tubular member.